Consolidated Financial Statement Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 97,060	$ 99,126
Accumulated depreciation	(90,418)	(92,380)
Total property and equipment, net	6,642	6,746
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	2,747	3,307
Asset retirement costs
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 2,307	2,307
Asset retirement costs | Minimum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	1 year
Asset retirement costs | Maximum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	5 years
Paging and computer equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 88,467	89,844
Paging and computer equipment | Minimum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	1 year
Paging and computer equipment | Maximum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	5 years
Furniture, fixtures and vehicles
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,539	$ 3,668
Furniture, fixtures and vehicles | Minimum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	3 years
Furniture, fixtures and vehicles | Maximum
Property, Plant and Equipment [Line Items]
Useful Life (In Years)	5 years